Because rapid development of drug resistance is a significant clinical problem and new antiviral drugs are needed, we are developing antiviral drugs that target HIV-1 integrase (IN) and determining their intracellular mechanisms of action. Through collaborative studies, we have identified azido-group containing beta-diketo acid derivatives (DKAs) as potent inhibitors of HIV-1 replication. We have also analyzed the effects of the DKAs on the frequency of 2-LTR circles as well as the sequences at the 2-LTR-circle junctions. These results suggest that the structure of the DKAs can influence the extent of degradation of viral DNA ends by host nucleases and the frequency of deletions at the 2-LTR-circle junctions. A suitable animal model system for testing of HIV-1 IN inhibitors is currently not available. We are constructing simian immunodeficiency virus (SIV)-HIV-1 hybrid viruses (SHIVs) that are dependent on the HIV-1 RT and IN for replication (SHIV-RT-IN). The SHIV-RT-IN viruses should provide a suitable animal model system to evaluate combination antiviral therapies containing anti-IN inhibitors alone or in combination with RT inhibitors and to characterize mutations in HIV-1 IN that confer resistance to the IN inhibitors. In collaboration with Dr. Kvaratskhelia's laboratory, we have performed mass spectrometric analysis to identify the HIV-1 IN binding site for a nucleotide analog inhibitor of HIV-1 IN, pyridoxal 5'-phosphate. These results indicate for the first time that a small inhibitor molecule can inhibit IN activity by binding to the protein C-terminus. In collaborative studies, we are exploring novel methods to identify lead compounds that inhibit HIV-1 IN. The purpose of the project is to discover candidate inhibitors of HIV-1 IN on the basis of latest technologies in bioinformatics and computer-aided drug design. The capability of all candidate compounds to inhibit HIV-1 integrase will be tested in vitro, and the most potent substances will be prepared in sufficient amounts. The promising lead compounds will be tested in the cell-based assays that we have developed to determine their ability to inhibit HIV-1 replication and to determine the molecular targets of antiviral activity. In conjunction with these studies, we are developing in vivo assays to define the intracellular mechanisms of action of HIV-1 IN inhibitors and are developing quantitative methods to determine the effects of potential HIV-1 IN inhibitors of 2-LTR circle formation. Finally, we are developing novel in vivo assays to identify new lead compounds that inhibit HIV-1 IN.